Due to advances in semiconductors and related technologies, light-emitting diodes (LEDs) have become so cost-effective as to make them feasible for lighting systems that previously relied upon incandescent or discharge lamps. Consequently, a substantial variety of LED-based replacement solutions have become available.
In the realm of household lighting, replacement of incandescent bulbs with bulbs that utilize LEDs has become commonplace. LED-based bulbs are still more costly than standard incandescent bulbs, but offer certain advantages, such as improved energy efficiency and much greater operating life.
In the realm of industrial lighting (e.g., factories and warehouses) and area lighting (e.g., office spaces and large residential spaces), the transition from conventional light sources to LED-based light sources has likewise proceeded at a fast pace. One of the major challenges has been the fact that many of those environments include large numbers of lighting fixtures which already include ballasts (magnetic and/or electronic) that are specifically designed for powering discharge lamps.
In recent years, many efforts have been directed to the challenge of providing LED-based light sources that are so-called “drop in” replacements for existing discharge lamps. These “drop-in” replacement LED-based light sources are commonly housed within a package resembling that of a conventional discharge lamp tube, and typically include a number of LEDs (arranged in various series, or series-parallel, combinations), along with associated circuitry, to functionally take the place of the discharge lamp(s) that they replace.
At least some of the existing LED-based replacements require, as a condition prior to installation, that the ballast(s) within the fixture at least be disconnected. As will be discussed in further detail herein, the need to disconnect the ballast(s) arises because of incompatibilities between the electrical requirements/behavior of the ballast(s) and those of the LED-based replacements. Disconnection of the ballast(s) involves laborious and costly rewiring and/or alteration of lighting fixtures, so that has been a significant impediment to the adoption of LED-based replacements.
There are some existing LED-based replacements that do not require disconnection of the ballast(s) within the fixture. Unfortunately, all known existing LED-based replacements are compatible with only a limited number of ballasts, and thus do not provide a “universal” retrofit solution. Additionally, as these existing replacements essentially introduce a capacitance in series with LEDs (so as to provide the impedance matching that is required for successful operation), that often leads to severe incompatibilities with ballasts which include certain types of protective circuitry; those incompatibilities usually result in the ballast either turning off (which keeps the LEDs from turning on in the first place) or, worse yet, turning off and on (which causes the LEDs to flash).
In contrast with what is required for powering LEDs, discharge lamps require ballasts in order to fulfill a number of essential functions that are particular to discharge lamps, the most essential of which are: (1) providing a high voltage for igniting the lamps; (2) providing a magnitude-limited source of current for properly operating the lamps; and (3) protecting the ballast circuitry from damage in the event of various fault conditions, such as what occurs due to wiring errors (e.g., output short-circuit conditions) or during times when the lamps themselves reach what are commonly referred to as “end of life” conditions.
Concerning the third ballast function (i.e, protecting the ballast circuitry from damage in the event of various fault conditions), it should be appreciated that LEDs exhibit an impedance characteristic that is quite different from that of discharge lamps. That difference is especially pronounced in the critical time period immediately following application of power. More specifically, LEDs exhibit a markedly lower impedance than discharge lamps, and that low impedance causes certain ballasts with advanced types of protection circuitry to preemptively shut down when the load is a LED-based replacement, instead of a particular type of discharge lamp for which the ballast was designed to power. The result is that no power is provided to the LEDs, since the ballast has shut down in response to a perceived output short condition. This is a serious problem which has yet to be fully resolved in the arts relating to LED-based replacements.
What is needed, therefore, is an improved drop-in replacement which does not require removal of existing ballasts; such a drop-in replacement should accommodate the fact that rewiring of the fixture is a substantial inconvenience and expense in applications for which substitution of discharge lamps with LED-based light sources would be an otherwise attractive alternative. A need also exists for a drop-in replacement that is compatible with a wide variety of existing ballasts, so as to provide a “universal” retrofit solution. A further need exists for a drop-in replacement which includes means for rendering it more fully compatible with ballasts that include protective circuitry for detecting and responding to short-circuit conditions in the initial period after the ballast first begins to operate. A drop-in arrangement with such means and advantages would represent a substantial improvement in the art.